This invention relates to safety apparatus for plastic molding machines and, more particularly, to safety apparatus that eliminates operator involvement in the operation of the machine from the time a fault is first detected until the time the fault is corrected.
This invention relates to safety apparatus having particular utility in rotary blow molding machines which produce molded articles, e.g., plastic bottles. In such machines, a hot plastic tube (parison) is continuously extruded from an extrusion die into circumferentially spaced molds mounted on the periphery of a ferris-wheel type supporting structure. Typically, the machine may include 14 molds and may rotate at a speed of 6 revolutions per minute. The parison is sequentially engaged by the molds which clamp off sections of the parison and sections extending between adjacent molds. The clamped off sections of the parison are sealed by the clamping action of the molds and air is injected into the sealed parison to expand it and cause it to conform to the contour of the molds. Further on in the rotation, the molds open to eject the blown plastic articles. The parison between the molds and connecting the blown articles is also separated from the machine for subsequent regrinding and reworking.
A practical feature of such machines is the fact that the parison is extruded continuously whether or not the machine is rotating. This provides for a homogeneous melt with a uniform heat profile. Because there is no interruption of the parison formation, there is less chance for degradation of the melt as it passes from the extruder through the die head.
There has been an attendant danger to the operator that occurs when, because of a fault in the operation, e.g. a blown article is not ejected, the machine will stop rotating and the production of the plastic article will be interrupted. The extruded parison, however, continues to flow into and accumulate in the mold located beneath the extruder. In order to remove the accumulated parison, the operator, wearing asbestos gloves, has got to first reach into the machine, manually remove the parison and then literally catch the flowing parison to prevent it from going into the mold. It will be appreciated that if the molds were to close on an excessive amount of parison located therein, the molds could suffer sever damage.
Once having removed the hot parison from the machine, the operator has got to wipe the die head clean and then very rapidly restart the machine. During the restarting cycle, the operator has both hands inside the machine in order to remove the excess parison. Because of this dangerous condition, the machine is throttled down to run at less-than-optimum speed and production is accordingly reduced.